Beck Alexander, Vogt Franziska, Hägele Lorena, Rupp Steffen, Zibek Susanne
Institute of Interfacial Process Engineering and Plasma Technology IGVP, University of Stuttgart, Stuttgart, Germany.
Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB, Stuttgart, Germany.
Front Bioeng Biotechnol. 2022 May 17;10:913362. doi: 10.3389/fbioe.2022.913362. eCollection 2022.
Mannosylerythritol lipids are glycolipid biosurfactants with many interesting properties. Despite the general interest in those molecules and the need for a robust process, studies on their production in bioreactors are still scarce. In the current study, the fermentative production of MEL in a bioreactor with was performed using a defined mineral salt medium. Several kinetic process parameters like substrate consumption rates and product formation rates were evaluated and subsequently enhanced by increasing the biomass concentration through an exponential fed-batch strategy. The fed-batch approaches resulted in two to three fold increased dry biomass concentrations of 10.9-15.5 g/L at the end of the growth phase, compared with 4.2 g/L in the batch process. Consequently, MEL formation rates were increased from 0.1 g/Lh up to around 0.4 g/Lh during the MEL production phase. Thus, a maximum concentration of up to 50.5 g/L MEL was obtained when oil was added in excess, but high concentrations of residual fatty acids were also present in the broth. By adjusting the oil feeding to biomass-specific hydrolysis and MEL production rates, a slightly lower MEL concentration of 34.3 g/L was obtained after 170 h, but at the same time a very pure crude lipid extract with more than 90% MEL and a much lower concentration of remaining fatty acids. With rapeseed oil as substrate, the ideal oil-to-biomass ratio for full substrate conversion was found to be around 10 g/g. In addition, off-gas analysis and pH trends could be used to assess biomass growth and MEL production. Finally, kinetic models were developed and compared to the experimental data, allowing for a detailed prediction of the process behavior in future experiments.
甘露糖赤藓糖醇脂是具有许多有趣特性的糖脂生物表面活性剂。尽管人们对这些分子普遍感兴趣，且需要一个稳健的生产过程，但关于它们在生物反应器中生产的研究仍然很少。在本研究中，使用限定的矿物盐培养基在生物反应器中进行了甘露糖赤藓糖醇脂（MEL）的发酵生产。评估了几个动力学过程参数，如底物消耗速率和产物形成速率，随后通过指数补料分批策略提高生物量浓度来增强这些参数。与分批过程中4.2 g/L相比，补料分批方法在生长阶段结束时使干生物量浓度增加了两到三倍，达到10.9 - 15.5 g/L。因此，在MEL生产阶段，MEL形成速率从0.1 g/(L·h)提高到了约0.4 g/(L·h)。因此，当过量添加油时，获得了高达50.5 g/L的MEL最大浓度，但肉汤中也存在高浓度的残留脂肪酸。通过将油进料调整为与生物量特定水解和MEL生产率相匹配，170小时后获得了略低的34.3 g/L的MEL浓度，但同时得到了一种非常纯的粗脂质提取物，其中MEL含量超过90%，残留脂肪酸浓度低得多。以菜籽油为底物，发现完全底物转化的理想油与生物量之比约为10 g/g。此外，废气分析和pH趋势可用于评估生物量生长和MEL生产。最后，开发了动力学模型并与实验数据进行比较，以便对未来实验中的过程行为进行详细预测。
